1. Field of the Invention
The present invention relates to a precombustion chamber in an internal combustion engine, and more particularly to a precombustion chamber in an internal combustion engine which ignites pilot quantities of an air/fuel mixture in order to ignite larger amounts of an air/fuel mixture within the main combustion chamber.
2. Description of the Related Art
Internal combustion engines with large reciprocating cylinders are commonly used in the oil and gas industry as prime movers for pipelines. These engines are also used in general industry to generate electric power. As with most internal combustion engines, a spark plug is employed to ignite the air/fuel mixture periodically in the engine cycle. However, as the size of the combustion chamber formed by the piston cylinder increases in diameter, the effectiveness of spark plugs to induce combustion is diminished. This is due in part because the arc generated by the spark plug is very localized. The situation is exacerbated when the air/fuel ratio is made lean in an effort to reduce emissions and increase fuel efficiency. In a large combustion chamber, for example, it may take an undesirable period of time for the combustion process to propagate throughout the combustion chamber.
To solve such ignition problems in large combustion chambers, precombustion chambers have been developed which can be connected to the main combustion chamber by a suitable passage. Precombustion chambers in natural gas, spark ignited, stratified charge engines can be used to initiate combustion in the lean air/fuel ratio main chamber. In this type of combustion system, small amounts of fuel are injected into the precombustion chamber. A spark plug or other means of ignition is energized, forming a flame kernel which ignites the rich charge in the precombustion chamber. The hot, burning combustion products from the precombustion chamber flow through the orifice into the main combustion chamber thereby igniting an air/fuel mixture previously injected into the main combustion chamber. Usually, if the precombustion chamber combustion is satisfactory (i.e., on time and complete) the main chamber combustion will be satisfactory. As the burning air and fuel and combustion products from the precombustion chamber occupy a much larger volume than the spark plug arc, the combustion process within the main combustion chamber is completed much more rapidly, resulting in greater engine efficiency.
However, in prior art engines having precombustion chambers, combustion of the precombustion charge has not been successful because the air/fuel mixture is admitted into the precombustion chamber from the main combustion chamber as a high velocity stream. High velocity flows, although turbulent, fail to mix the burned fuel, unburned fuel, and air sufficiently to ensure consistent precombustion chamber combustion near the spark plug gap. Poor mixing of the burned fuel, unburned fuel and air can cause inconsistent combustion because there is not always a combustible mixture at the spark plug gap. Consequently, inconsistent precombustion chamber combustion causes the main chamber combustion to occur either too early, too late, too slowly, or not at all, resulting in lower engine efficiency and higher toxic exhaust emissions.
Inconsistencies in precombustion chamber combustion and in the hot gasses generated are particularly problematic when natural gas is used as the fuel with a lean air/fuel mixture, resulting in inconsistent main combustion chamber firing. The natural variability of the constituents in natural gas can introduce inconsistencies in burning, as different constituents burn hotter or colder in the engine. Further, a lean air/fuel ratio can increase the likelihood of inconsistencies in burning because there is a smaller margin of fuel in the combustion chamber in excess of that amount necessary for proper combustion. Particularly if the fuel is not mixed sufficiently, there can be regions of gas near the spark plug gap at the time of combustion that do not contain sufficient fuel for consistent burning.
A partial solution to some of the aforementioned problems is described in U.S. Pat. No. 4,594,976 to Gonzalez which discloses a hybrid internal combustion reciprocating engine including a prechamber connected to the main combustion chamber by means of a passage or orifice located in such a manner as to induce a swirling airflow within the prechamber during the compression stroke. The Gonzalez invention, however, suffers from a problem similar to other precombustion chamber engines in which high velocity gas is injected into the precombustion chamber. That is, the combustion process is disrupted when the spark plug gap is located in a high gas velocity region of the precombustion chamber. A high gas velocity at the spark plug gap inhibits rapid propagation of the combustion process throughout the precombustion chamber.
Typically, the combustion inside precombustion chambers is difficult to initiate and maintain consistently because the gas flow within the precombustion chamber is so fast and unorganized that the flame kernel (the small burning air and fuel mixture just after the spark plug first ignites it) is often forced against a cold wall in the chamber which either extinguishes this small flame kernel completely, resulting in a complete misfire, or causes a long delay before the kernel grows enough to light off the rest of the unburned precombustion chamber charge.
By contrast, good consistent ignition occurs when the mixture at the spark plug gap is low in velocity and at a stoichiometric air-fuel ratio, where complete burning of the fuel occurs. These conditions allow the flame kernel to grow to sufficient size and strength to ignite the rest of the unburned charge.
Prior art engines have also failed to include means for dispersing the ignited gas over a broad area in the main combustion chamber. Instead, the ignited gas from the precombustion chamber has been supplied to the main combustion chamber through a single small opening. Consequently, the period of propagation of the combustion process throughout the main combustion chamber has been unacceptably long in duration, especially in large main combustion chambers, resulting in inefficient and inconsistent firing.
There is, therefore, a need in the art for an internal combustion engine with a precombustion chamber which burns pilot fuel and air consistently, evenly and efficiently and which prevents overheating of the spark plug unit. Further, there is a need in the art for an engine with a precombustion chamber that provides a consistently well-mixed, low velocity air/fuel mixture at the spark plug gap, and which broadly distributes the ignited gas throughout the main combustion chamber.